In general, in a manufacturing process of semiconductor integrated circuits, various single-substrate processes, such as a film forming process, an etching process, a heat treatment process, a quality modification process, a crystallization process, are repeated on a target object such as a semiconductor wafer to build up the desired integrated circuits. In the various processes described above, required gases corresponding to specific processes, e.g., a film forming gas for the film forming process, an ozone gas or the like for the quality modification process, and an O2 gas or an inactive gas such as N2 for the crystallization process, are introduced into processing chambers.
For example, in case of a single-wafer heat treatment apparatus which performs heat treatment on semiconductor wafers on a single wafer basis, a mounting table which includes, e.g., a built-in resistance heater or the like is installed in a vacuum-evacuable processing chamber and a semiconductor wafer is mounted on the top surface of the mounting table. Under these circumstances, a processing gas is introduced into the processing chamber, and heat treatment is variously performed on the semiconductor wafer under a process condition (see, for example, Japanese Patent Laid-open Application No. 2002-256440).
In a heat treatment apparatus of a different type, an inner processing chamber made of, e.g., quartz glass is provided in a vacuum-evacuable processing chamber made of, e.g., aluminum, and a substrate supporting table which includes a built-in resistance heater is prepared in the inner processing chamber. The inner processing chamber is supplied with a plurality of processing gases of different species flowing alternately in an intermittent manner. Hence, thin films each being about one molecular layer in thickness can be repeatedly laminated on the surface of the semiconductor wafer supported on the substrate supporting table (see, for example, Japanese Patent Laid-open Application No. 2002-151489).
However, it is required to make each layer thinner as well as to make the line width narrower in accordance with the high integration and the high miniaturization of the semiconductor integrated circuits. Under the circumstances, stricter standards for contamination, such as organic contamination and metal contamination, are also required. Therefore, structures in the processing chamber are made of purer materials which do not contain metal species serving as a source of contamination. The structures in the processing chamber include, e.g., a heater for heating a semiconductor wafer or the like, and a mounting table which supports a wafer. A mounting table was also proposed, wherein a heater is completely covered with high purity quartz plates and/or quartz cases thermally bonded as a single unit (see Japanese Patent Laid-open Application No. S63-278322, Japanese Patent Laid-open Application No. H07-078766, Japanese Patent Laid-open Application No. H03-220718, or Japanese Patent Laid-open Application No. H06-260430).
To encapsulate the whole heater inside the quartz plates and/or the quartz cases, planar quartz surfaces are required to be thermally bonded together. Therefore, quartz needs to be machined with good flatness. That is, surface processing of quartz is needed with high accuracy. Such a process, however, is very difficult, and the apparatus itself becomes costly.
Further, in case of using transparent quartz material, thermal efficiency becomes poor since heat rays from the heater buried inside the quartz radiate in all directions.
Moreover, if the heater material contains metal atoms of, e.g., heavy metals, a semiconductor wafer can be contaminated by such metal atoms even when the heater is completely encapsulated with quartz. That is because such metal atoms can move across the quartz by so-called thermal diffusion.